Dynamic cardiorespiratory interaction during head-up tilt-mediated presyncope

Krishnamurthy, S.; Wang, X.; Bhakta, Divyesh; Bruce, Eugene N.; Evans, Joyce M.; Justice, Todd; Patwardhan, Abhijit

doi:10.1152/ajpheart.00485.2004

Cited by 19 publications

(16 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In summary, the independence of fluctuations in RAP from corresponding changes in ABP and CBFV is demonstrated by the possibility of an infinite number of RAP values for each mean [ABP, CBFV] pair. For the ABP ϩ RAP inputs, the population mean multiple coherence is significantly less than unity but reaches values Ͼ0.7 for frequencies Ͻ0.05 Hz, and this is much higher than the typical values of ϳ0.4, or less, that we and others have found for the standard coherence between ABP and CBFV (10,14,18,29,35,37,40,41).…”

Section: Discussioncontrasting

confidence: 55%

Multiple coherence of cerebral blood flow velocity in humans

Panerai¹,

Eames²,

Potter³

2006

American Journal of Physiology-Heart and Circulatory Physiology

View full text Add to dashboard Cite

The coherence function has been used in transfer function analysis of dynamic cerebral autoregulation to assess the statistical significance of spectral estimates of gain and phase frequency response. Interpretation of the coherence function and choice of confidence limits has not taken into account the intrinsic nonlinearity represented by changes in cerebrovascular resistance due to vasomotor activity. For small spontaneous changes in arterial blood pressure (ABP), the relationship between ABP and cerebral blood flow velocity (CBFV) can be linearized, showing that corresponding changes in cerebrovascular resistance should be included as a second input variable. In this case, the standard univariate coherence function needs to be replaced by the multiple coherence, which takes into account the contribution of both inputs to explain CBFV variability. With the use of two different indicators of cerebrovascular resistance index [CVRI ϭ ABP/CBFV and the resistance-area product (RAP)], multiple coherences were calculated for 42 healthy control subjects, aged 20 to 40 yr (28 Ϯ 4.6 yr, mean Ϯ SD), at rest in the supine position. CBFV was measured in both middle cerebral arteries, and ABP was recorded noninvasively by finger photoplethysmography. Results for the ABP ϩ RAP inputs show that the multiple coherence of CBFV for frequencies Ͻ0.05 Hz is significantly higher than the corresponding values obtained for univariate coherence (P Ͻ 10 Ϫ5 ). Corresponding results for the ABP ϩ CVRI inputs confirm the principle of multiple coherence but are less useful due to the interdependence between CVRI, ABP, and CBFV. The main conclusion is that values of univariate coherence between ABP and CBFV should not be used to reject spectral estimates of gain and phase, derived from small fluctuations in ABP, because the true explained power of CBFV in healthy subjects is much higher than what has been usually predicted by the univariate coherence functions. cerebral autoregulation; coherence function; transfer function analysis; multivariate modeling; transcranial Doppler ultrasound TRANSFER FUNCTION ANALYSIS (TFA) is a useful technique to study physiological systems whose properties are characterized by linear or quasi-linear dynamic relationships between two or more physiological time series (6, 36). One area that has benefited from this approach is the study of dynamic cerebral blood flow (CBF) autoregulation in humans (27,28,40). Aaslid et al. (2) have extended the classical concept of "static" autoregulation (20) by showing that a sudden change in arterial blood pressure (ABP) leads to a relatively fast recovery of CBF to its original level. This transient response of the autoregulatory mechanisms is what is now termed "dynamic" cerebral autoregulation (CA) (2). TFA of dynamic CA was initially proposed by Giller (13), who modeled CA as an input-output relationship between beat-to-beat values of ABP and CBF, as estimated by transcranial Doppler ultrasound (TCD) recordings of CBF velocity (CBFV). The many contributions that followed...

show abstract

Section: Discussioncontrasting

confidence: 55%

Multiple coherence of cerebral blood flow velocity in humans

Panerai¹,

Eames²,

Potter³

2006

American Journal of Physiology-Heart and Circulatory Physiology

View full text Add to dashboard Cite

show abstract

“…14 employed a multivariate embedding approach, and Krishnamurthy et al 29 investigated coherence spectrum of heart rate variability and respiration.…”

Section: Discussionmentioning

confidence: 99%

Quantification of Cardiorespiratory Interactions Based on Joint Symbolic Dynamics

et al. 2011

View full text Add to dashboard Cite

Abstract-Cardiac and respiratory rhythms are highly nonlinear and nonstationary. As a result traditional time-domain techniques are often inadequate to characterize their complex dynamics. In this article, we introduce a novel technique to investigate the interactions between R-R intervals and respiratory phases based on their joint symbolic dynamics. To evaluate the technique, electrocardiograms (ECG) and respiratory signals were recorded in 13 healthy subjects in different body postures during spontaneous and controlled breathing. Herein, the R-R time series were extracted from ECG and respiratory phases were obtained from abdomen impedance belts using the Hilbert transform. Both time series were transformed into ternary symbol vectors based on the changes between two successive R-R intervals or respiratory phases. Subsequently, words of different symbol lengths were formed and the correspondence between the two series of words was determined to quantify the interaction between cardiac and respiratory cycles. To validate our results, respiratory sinus arrhythmia (RSA) was further studied using the phase-averaged characterization of the RSA pattern. The percentage of similarity of the sequence of symbols, between the respective words of the two series determined by joint symbolic dynamics, was significantly reduced in the upright position compared to the supine position (26.4 ± 4.7 vs. 20.5 ± 5.4%, p < 0.01). Similarly, RSA was also reduced during upright posture, but the difference was less significant (0.11 ± 0.02 vs. 0.08 ± 0.01 s, p < 0.05). In conclusion, joint symbolic dynamics provides a new efficient technique for the analysis of cardiorespiratory interaction that is highly sensitive to the effects of orthostatic challenge.

show abstract

“…For the current analysis, only frequency domain analyses were employed. An autoregressive model was used to calculate the RR interval spectrum, BP power spectrum, and cross spectrum (13)(14)(15). In brief, RR intervals and BP, acquired as a sequence of discrete point events, were transformed into an impulse train in which pulses were arranged at equal intervals (equal to the mean RR interval) with impulse heights equal to the RR intervals or BP as appropriate.…”

Section: Details Of Methodsmentioning

confidence: 99%

“…Other possibilities include a primary abnormality in chemoreflex response or ventilatory control in these patients, but there is little evidence for either of these during supine rest (13), suggesting that there is no intrinsic defect in chemoreception in these patients.…”

mentioning

confidence: 95%

Postural hypocapnic hyperventilation is associated with enhanced peripheral vasoconstriction in postural tachycardia syndrome with normal supine blood flow

Stewart¹,

Medow²,

Cherniack³

et al. 2006

American Journal of Physiology-Heart and Circulatory Physiology

View full text Add to dashboard Cite

Previous investigations have demonstrated a subset of postural tachycardia syndrome (POTS) patients characterized by normal peripheral resistance and blood volume while supine but thoracic hypovolemia and splanchnic blood pooling while upright secondary to splanchnic hyperemia. Such "normal-flow" POTS patients often demonstrate hypocapnia during orthostatic stress. We studied 20 POTS patients (14-23 yr of age) and compared them with 10 comparably aged healthy volunteers. We measured changes in heart rate, blood pressure, heart rate and blood pressure variability, arm and leg strain-gauge occlusion plethysmography, respiratory impedance plethysmography calibrated against pneumotachography, end-tidal partial pressure of carbon dioxide (Pet(CO2)), and impedance plethysmographic indexes of blood volume and blood flow within the thoracic, splanchnic, pelvic (upper leg), and lower leg regional circulations while supine and during upright tilt to 70 degrees. Ten POTS patients demonstrated significant hyperventilation and hypocapnia (POTS(HC)) while 10 were normocapnic with minimal increase in postural ventilation, comparable to control. While relative splanchnic hypervolemia and hyperemia occurred in both POTS groups compared with controls, marked enhancement in peripheral vasoconstriction occurred only in POTS(HC) and was related to thoracic blood flow. Variability indexes suggested enhanced sympathetic activation in POTS(HC) compared with other subjects. The data suggest enhanced cardiac and peripheral sympathetic excitation in POTS(HC).

show abstract

Dynamic cardiorespiratory interaction during head-up tilt-mediated presyncope

Cited by 19 publications

References 23 publications

Multiple coherence of cerebral blood flow velocity in humans

Multiple coherence of cerebral blood flow velocity in humans

Quantification of Cardiorespiratory Interactions Based on Joint Symbolic Dynamics

Postural hypocapnic hyperventilation is associated with enhanced peripheral vasoconstriction in postural tachycardia syndrome with normal supine blood flow

Contact Info

Product

Resources

About